The present invention is directed to a butterfly valve and, more particularly, to a new and improved high performance, leak tight seal for a butterfly control valve.
Typically, a butterfly valve comprises a vane in the form of a disc with a part sherical periphery. The disc is rotatably mounted within the fluid path of a valve housing, whereby the vane periphery may be rotated to engage the internal surfaces of the housing to shut the valve. When in the closed position, it is desirable to provide a seal element between the vane periphery and valve housing surface to insure a leak tight valve shut off. Accordingly, the prior art contains numerous proposals for a seal element construction suitable for sealing the vane of a butterfly valve. Typically, the seal element is in the form of a ring seal that extends circumferentially about the valve housing at the position where the vane periphery is rotated at the valve shut off. The seal engages the vane periphery and applies a radial squeeze thereon to seal the valve. The prior art includes seals having glass filled membranes to provide dimensional stability to the seal element during operation of the valve. In addition, many previous proposals for a butterfly valve seal utilize additional spring elements arranged to impart a radial squeeze by the seal on the vane periphery.
It is a primary objective of the present invention to provide a new and improved seal element for use in a high performance butterfly control valve. Generally, the seal element comprises an annular seal element formed to a predetermined cross section including three integral portions. The middle portion is arranged to extend relative to the upper first portion and lower third portion in the upstream fluid flow direction, and the first portion only is securely mounted within a seal containment chamber which generally surrounds and conforms to the predetermined cross section of the seal element. The third portion is arranged to extend from the seal containment chamber and into the fluid flow path of the valve housing whereby the third portion may engage the periphery of the vane at valve shut off to provide a leak tight seal.
Pursuant to a significant feature of the invention, fluid pressure will be retained by the seal element through three clearly defined discrete pressure range operating stages of the seal element. During each of the discrete pressure range operating modes of the seal element, the fluid pressure will inherently and automatically orient the seal relative to the seal containment chamber to provide a seal geometry, containment chamber support, stress distribution and seal deflection which is optimum for the pressure range of the particular operating mode. In this manner, the pressure effects upon the seal element are maintained at a practical minimum for each of the three discrete pressure ranges to considerably reduce wear and tear on the seal element and thereby greatly extend the worklife of the seal of the invention. Significantly, the present invention teaches a seal element that achieves leak tight valve shut off over a long worklife without the need of glass filled internal membranes for dimensional stability or additional spring elements to impart a radial squeeze.
For a better understanding of the above, and other features and advantages of the invention, reference should be made to the following detailed description of a preferred embodiment of the invention and to the accompanying drawings.